Due to increased traffic on the Internet, many web sites now comprise a series of redundant servers controlled by a switch. FIG. 1 is a diagram illustrating an example of a computer network with redundant servers. The plurality of redundant servers 104a-104e are managed by a switch 102, which may direct traffic from a user 100 to an appropriate server based on various Quality of Service (QoS) parameters. For example, the switch 102 may perform load balancing, where traffic is directed to servers that are best able to handle the bandwidth and processor load required at the time the traffic is received.
In certain circumstances, however, it is beneficial to route traffic from a single user to the same server or server group each time a transaction (which may include a request and a response) is made. Normally, however, the traffic is routed based solely on the current server load. One solution to this would be to examine the source of the traffic (i.e., the user's IP address) and use that information to route the traffic to the same server or server group as was used in the last transmission.
Unfortunately, it is not always possible to distinguish individual users by their IP address, such as where network address translation is used (NAT). For these cases, it may be helpful to utilize cookies to identify individual users. When a client makes a request from a server, the response from the server can contain a cookie embedded into the Hypertext Transport Protocol (HTTP) header of the response. The client may then store the cookie and, upon subsequent requests, place the cookie into the HTTP header of the request. The server may then perform cookie switching for any HTTP request containing a cookie, routing the request to an appropriate server identified by the cookie.
Some companies, however, would need to significantly alter the software code running on their servers in order to provide for the ability to generate cookies. For these companies, a solution wherein the switch itself generated the cookies would be more beneficial. In this implementation, the switch would introduce a cookie to the HTTP response when it receives it, before forwarding it back to the user. Each incoming HTTP request would be examined to determine if a valid cookie identifies a preferred server for routing, and route the request accordingly.
Several problems, however, are introduced by such an implementation. First, it may sometimes be necessary for a particular cookie to be deleted from the user's computer, for example if the corresponding server is down or has been removed from the system. However, currently no mechanism exists allowing the switch to indicate that a cookie should be deleted from the user's computer. Furthermore, some companies may have software that is incompatible with cookies, even to such an extent as to crash or otherwise interfere with the performance of the software if an http request is received containing a cookie, even if the software is not planning on doing anything with the cookie. Currently, no mechanism exists for removing the cookie before it arrives at such a company's server. Therefore, a need exists for a solution that can overcome these problems.